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Meiosis. Box 55. Meiosis results in cells with ½ the # of chromosomes, so they can combine in sexual reproduction , which results in an embryo with the normal amount of chromosomes.

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meiosis
Meiosis

Box 55

Meiosis results in cells with ½ the # of chromosomes, so they can combine in sexual reproduction, which results in an embryo with the normal amount of chromosomes.

  • To solve this problem, the cells in the gametes (eggs and sperm), undergo Meiosis instead of Mitosis, when they divide.
  • Why Meiosis?
  • Most cells in our body are Diploid (“di” = 2)
  • Diploid = have 2 sets of chromosomes, 2n(one from mom, one from dad)
  • Sex cells, or gametes, are Haploid
  • Haploid = have 1 set of chromosomes, 1n

Box 53

Box 41

Box 54

Box 42

chromosome number
Chromosome Number

Box 56

Homologous chromosomes= 2 sets of similar chromosomes, one from mom, one from dad

  • An example.
  • Fruit Flies (Drosophila), have 8 chromosomes total – 4 from dad fruit fly, 4 from mom fruit fly.

Box 43

2n = 8

Diploid number?

Haploid number?

1n = 4

phases of meiosis
Phases of Meiosis

Homologous = same chromosome, it just comes from different parents (mom or dad)

  • How are haploid (1n) gamete cells produced from diploid (2n) cells?
  • By Meiosis (my-OH-sis)
  • Meiosis = process of reduction cell division where the # of chromosomes per cell is cut in ½ by the separation of homologous chromosomes

Box 57

Box 45

Box 58

Box 46

  • Meiosis involves 2 distinct divisions,
  • Meiosis I
  • Meiosis II
  • Results of Meiosis? = cells with a haploid (1n) number of chromosomes

Box 59

meiosis i
Meiosis I

Box 61

Prophase I = Each chromosome pairs up with its matching homologous chromosome forming a tetrad

Interphase I = Cells undergo a round of DNA replication, forming duplicate chromosomes

Tetrads= in prophase I, chromosomes duplicate and form a structure with 4 chromosomes (tetrad)

Box 60

Box 62

4 sister chromatids form a Tetrad

2 sister chromatids

Interphase I

Prophase I

Chromosome duplication

slide5

During prophase I of Meiosis, when the tetrads form, a phenomenon called “Crossing Over” can occur.

Crossing Over = results in the exchange of genetic information between homologous chromosomes

Box 63

You got peanut butter in my chocolate!

You got chocolate in my peanut butter!

Sorry!

Hey hot stuff, wanna dance?

Owww! My arm!

Who me?

I think he likes me!

Help!

meiosis i1
Meiosis I

Anaphase I = Fibers pull the homologous chromosomes towards opposite ends of the cell (“A” for apart)

Prophase I = Each chromosome pairs up with its corresponding homologous chromosome to form a tetrad

Box 64

Metaphase I = Spindle fibers attach to the chromosomes, then they line up in the middle (“M” for middle)

Interphase I = Cells undergo a round of DNA replication, forming duplicate chromosomes

Box 65

Interphase I

Prophase I

Metaphase I

Anaphase I

meiosis i2
Meiosis I

Anaphase I = Fibers pull the homologous chromosomes towards opposite ends of the cell (“A” for apart)

Prophase I = Each chromosome pairs up with its corresponding homologous chromosome to form a tetrad

Metaphase I = Spindle fibers attach to the chromosomes, then they line up in the middle (“M” for middle)

Telophase I and Cytokinesis = Nuclear membranes form, the cell separates into 2 new cells

Interphase I = Cells undergo a round of DNA replication, forming duplicate chromosomes

Box 66

Interphase I

Prophase I

Metaphase I

Anaphase I

Telophase and Cytokinesis

meiosis ii
Meiosis II

Prophase II = of meiosis I results in 2 haploid daughter cells, each with ½ the # of chromosomes as the original cell

Box 67

The 2 new cells now enter a 2nd round of meiotic division

No more chromosome duplication

prophase II

meiosis ii1
Meiosis II

Metaphase II = chromosomes line up in the middle

Box 68

metaphase II

prophase II

Prophase II = of meiosis I results in 2 haploid daughter cells, each with ½ the # of chromosomes as the original cell

meiosis ii2
Meiosis II

Anaphase II = sister chromatids separate and move to opposite ends of the cell

Box 69

Prophase II = of meiosis I results in 2 haploid daughter cells, each with ½ the # of chromosomes as the original cell

Metaphase II = chromosomes line up in the middle

Telophase II and Cytokinesis = of meiosis II results in 4 haploid (1n) daughter cells

Box 70

4

3

metaphase II

anaphase II

telophase II

prophase II

2

1

slide11

Flow Chart for Meiosis

I

P

Interphase I

M

Prophase I

A

Metaphase I

Anaphase I

T

92

Telophase I

&Cytokinesis

92

92

92

Humans = 2n = 46

46

P

Prophase II

A

M

T

Telophase II

&

Cytokinesis

Anaphase II

Metaphase II

46

23

46

46

4 daughter cells

with haploid # (1n)

I then …PMAT…..PMAT

gamete formation
Gamete Formation

For Sexual Reproduction, where egg and sperm unite to make an embryo

Box 72

  • Why do we even have Meiosis?
  • To make gametes (eggs and sperm).
  • Male gametes = sperm
  • Female gametes = eggs

Box 71

Skip Box 59

Why do we need eggs and sperm?

End of Chapter 10 and Chapter 11 Section 11-4